The invention relates to a fuel injector for use in a liquid rocket engine, and more particularly to an injector element which has been designed to provide a low pressure drop through the injector for increased thrust and combustion efficiencies.
In the past coaxial type injector elements have been used in the main injector assembly of liquid propellant rocket engines for space vehicles such as the space shuttle vehicle. The prior injector assembly and injector elements have utilized baffles and helmholz resonators to dampen oscillations and provide for more stable and efficient combustion.
In addition, the metering orifice for the liquid oxygen in the prior main injector elements has been at the inlet end of the injector element making it difficult to replace or change the size of the metering orifice to vary the mixture ratio. The injector elements themselves are welded in tightly and are very difficult, if not impossible, to replace without a major overhaul of the engine.
In the prior main injector assembly of the engine for the space shuttle vehicle, two types of main injector elements have been required due to the use of baffle elements. The baffle elements are used on a number of the injector elements and extend into the combustion chamber. While the baffle elements have been employed to provide stability of combustion, they also affect the combustion efficiency in an adverse way. Thus, not only has the prior design required two different types of injector elements, but their use has had both a positive and adverse effect.
Additionally, the lateral inflow of the hot gases from the turbine exhaust has caused overloading of the post of the injector element which can result in fractures of the injector elements. When the post of the injector element fractures, the liquid oxygen escapes causing lox (liquid oxygen) fires.
Various other elements having coaxial passages have been known prior to the present invention. For example, U.S. Pat. No. 4,036,434 discloses a nozzle for delivering a low velocity primary fuel having three major passages. It is a coaxial arrangement with a center passage providing a core stream and a coaxial passage which provides the fuel. A second coaxial passage is provided which delivers a purging fluid through a porous membrane at the primary face plate of the combusion chamber. The principal arrangement is different from the instant invention and generally unrelated to rocket engine fuel injectors.
U.S. Pat. No. 3,740,946 relates to a throttling injector for a liquid rocket engine which provides a desired pressure drop. The throttling valve varies the propellant flow to produce a momentum change. This is a different operating function and the throttling arrangement would not be suitable in a rocket engine environment.
U.S. Pat. No. 3,615,054 discloses a wafer construction which produces a misted type of injection. A fuel mist and an oxidizer mix a short distance from the combusion chamber face and achieve a low velocity mixing. This basic arrangement is quite different from coaxial injection and high velocity mixing of the instant invention.
The above patents do not disclose annular type injection which characterizes the injection element of the present invention wherein two concentric annuli adjacent to each other are applied for better mixing.
Accordingly, an important object of the present invention is to provide a main injector element for the main injector assembly of a liquid rocket engine having low pressure losses through the element for increased thrust.
Another important object of the present invention is to provide a main injector element for a liquid rocket engine which provides a more stable combustion pattern at the face plate of the main injector assembly.
Another important object of the present invention is to provide a larger diameter injector element with a communicating and resistive diametrical face path for good stability to avoid the use of baffle elements and thus increase combustion specific impulse.
Another important object of the present invention is to provide a main injector element for a main injector assembly which has a lox post having a larger diameter and wall thickness for reduced stresses caused by the lateral inflow of hot gases to avoid post fractures.
Still another important object of the present invention is to provide a main injector element for the main assembly of a liquid rocket engine which has metering orifices which can be easily replaced and exchanged to vary the mixture ratio.
Still another important object of the present invention is to provide a fuel injection element which has annular coaxial fuel passages dimensioned to produce a low pressure drop through the annulus for providing increased thrust.
Still another important object of the present invention is to provide larger diameter elements of larger clearances less sensitive to tolerances and less sensitive to clogging by contamination and soot.
Still another important object of the present invention is to provide a main injector assembly having a plurality of main injector elements which are easily maintainable and have a long life, and in which parts of the element may be replaced to increase the enhanced life of the injector element without excessive labor or engine outage.